Foams in aqueous systems are formed because amphiphilic and thus surface-active surfactant molecules accumulate at the water/gas interface and lead to a decrease in the surface tension. Owing to the resulting decreased surface tension, a new water/gas interface (=foam) is easily created. In addition, the foam formed in an aqueous system is stabilized by the surfactants by means of various mechanisms.
Mention may be made here by way of example of the Gibbs-Maragoni effect which is known to those skilled in the art and also the electrostatic or steric repulsion of surfactant molecules at reduced foam lamella thickness. The antifoams developed for these aqueous surfactant systems influence these stabilization mechanisms in various ways in which, for example, the displacement and deactivation of the surfactant molecules at the water/gas interface plays a role.
In contrast to aqueous systems which are to be regarded as mostly non-ionic, surfactant-stabilized systems the stabilization of the foam of an ionic liquid occurs by mechanisms different from those operating in an aqueous system. It should, in particular, instead resemble the stabilization of the foams of organic nonaqueous oils (e.g. diesel oil) which occurs by means of impurities having nonsurfactant character.
Ionic liquids are used and have been proposed for numerous applications in which gases, in particular air or nitrogen and other industrial gases, and also, for example, steam are introduced under shear. This results in foam formation which in many cases has adverse effects on the application (e.g. material wear due to increased friction). As such, a need still exists in the art to reduce or eliminate foam from ionic liquids.